This invention relates to a practical method of cold forming axially crowned working surfaces on the teeth of spur gears or the like starting with a sintered powder metal compact in the general shape of the desired gear, but slightly oversize. More particularly, this invention relates to a method of forming gear teeth having axially crowned working faces and at the same time sizing the gear to desired dimensions by upsetting a sintered powder metal gear compact.
Gear teeth having axially crowned working faces are well-known. Axially crowned gear teeth differ from normal gear teeth in that each tooth is thinner at the ends than at the center of the gear face. In other words, the gear working faces are convexly curved so that the gear tooth appears to bulge out at the center of the gear. Thus, when axially crowned spur gears interact, the working faces contact at the bulged center portion and not at the ends of the gear teeth. The principal advantages of axially crowning is that the gear develops a better wear pattern and theoretically is able to accept a greater load. An auxiliary advantage is that crowned gears operate at reduced noise levels. These benefits are obtained from even slight crowning. Working faces convexly curved as little as 0.0003 inch per inch of face width are generally sufficient for most applications.
Until now crown gears have been produced by machining operations such as hobbing and shaving. The principal disadvantage of machining gears is that such operations are complicated, slow and expensive.
It is therefore an object of this invention to provide a method of forming spur gears having teeth with axially crowned working faces that does not require machining to shape the tooth profile. It is also an object of this invention to provide equipment by which such gears may be formed faster and cheaper than by machining.
More specifically, it is an object of this invention to produce by a cold forming process axially crowned spur gear teeth from oversized sintered powder metal gear shaped compacts having gear teeth that are not crowned in the axial direction.
It is a further object of this invention to provide a method for forming crowned gear teeth and at the same time finish sizing the gear to desired dimensions by a restrike operation performed on sintered powder metal gear compacts.